Hey guys, my wife's Sport Trac's brake fluid reservoir is getting pretty low and there is no evidence of a leak. I have heard that as the brakes wear down the fluid will go down accordingly. True or false? :confused: Any ideas why the fluid would be low and there be no leaks? It's been a while since the brakes were replaced. No scrapping of wear indicatiors though. Thanks for any suggestions/thoughts. :grinyes:

It is true that as the friction material wears, the brake fluid will make up for most of that space by remaining in the caliper piston cylinder bore. The caliper pistons do not retract to a set position each time the brake pedal is released. Rather, they retract just enough so that the brake pads are not rubbing aggressively on the rotors. That is why the pistons need to be compressed when installing new brake pads. If you were to fill the master cylinder reservoir to the full line with worn pads, when the calipers were compressed to install new pads, if the bleeder screws were not opened to compress the pistons, the master cylinder reservoir would overflow.

The same goes for wheel cylinders if you have drum rear brakes, but the cylinder bore is much smaller and less fluid remains in them accordingly.

-Rod

Thanks big guy. :smile: Makes total sense. Looks like it is brake job time!